1. Field of the Invention
The present invention relates to a liquid crystal display device equipped with a flat display, such as a portable information terminal, a personal computer, a word processor, amusement equipment, and TV sets, viewed by a plurality of people; and a liquid crystal device used for a display plate, a window, a door, a wall, or the like utilizing a shutter effect and a method for producing the same.
2. Description of the Related Art
Conventionally, liquid crystal devices utilizing various display modes have been developed for commercial use; for example, a TN (twisted nematic) mode, an STN (super twisted nematic) mode, and the like performing a display utilizing electro-optic effects of a birefringent mode, and using nematic liquid crystal have been generally used. These modes require the use of polarizing plates and alignment treatment. Liquid crystal molecules in liquid crystal devices under these modes have a pretilt in an initial orientation state as shown in FIG. 58A. As shown in FIG. 58B, the liquid crystal molecules rise in the same direction when a voltage is applied to a cell. Because of this, an apparent refractive index and a display contrast vary depending upon viewing directions A and B. Furthermore, a display quality remarkably decreases depending upon viewing angles in gray scales as shown in FIG. 58B; specifically, inversion phenomenon and the like occur. In recent years, liquid crystal devices driven in an FCL (ferroelectric liquid crystal) display mode have been marketed. FIG. 58C shows the case where a saturated voltage is applied.
In recent years, devices not requiring polarizing plates and alignment treatment have been proposed. In such devices, a transparent state or an opaque state is electrically controlled using the birefringence of liquid crystal molecules. According to this method, the ordinary refractive index of liquid crystal molecules is matched with the refractive index of a supporting medium, and a transparent state is displayed when the liquid crystal molecules are aligned under the application of a voltage and an opaque state (light scattering state) is displayed when the orientation of the liquid crystal molecules is disturbed under no application of a voltage.
As examples of the above-mentioned method, Japanese National Publication No. 58-501631 discloses a method for including liquid crystal in polymer capsules and Japanese National Publication No. 61-502128 discloses a method in which liquid crystal and a photocurable resin or a thermosetting resin are mixed and the resin is cured, whereby the liquid crystal is deposited to form liquid crystal droplets in the resin. Devices produced by these methods are called polymer dispersed liquid crystal devices.
As a device having improved viewing angle characteristics using polarizing plates, Japanese Laid-Open Patent Publication Nos. 4-338923 and 4-212928 disclose a device in which the above-mentioned polymer dispersed liquid crystal device is interposed between polarizing plates positioned so that polarizing axes are orthogonal to each other. This device has an effect of improving viewing angle characteristics; however, it utilizes depolarization due to light scattering, so that brightness is as much as 1/2 lower as that of a TN-mode. Thus, this device has low use importance.
Furthermore, Japanese Laid-Open Patent Publication No. 5-27242 discloses a method in which the orientation state of liquid crystals is disturbed with polymer walls and projections to form random domains, whereby viewing angle characteristics are improved. However, according to this method, since domains are random and a polymer material comes in pixel portions, light transmittance under no application of a voltage is low. In addition, since disclination lines are randomly formed between liquid crystal domains and do not disappear under the application of a voltage, a black level under the application of a voltage is low. For these reasons, this device has a low contrast.
The applicant of the present application proposes a liquid crystal device in which liquid crystal molecules are axis-symmetrically aligned in polymer walls 4. Such a device is obtained by irradiating UV-rays having a regular irradiation pattern to a liquid crystal cell with a mixture of liquid crystal and a resin material injected thereto and allowing the liquid crystal and the resin material to be regularly phase-separated. In this device, as shown in FIG. 58D, since liquid crystal molecules 3a are axis-symmetrically aligned in liquid crystal regions 3, a display contrast does not change and hence, inversion phenomenon does not occur even when the cell is observed in different viewing directions A and B as shown in FIG. 58E, viewing angle characteristics can be remarkably improved. FIG. 58F shows the case where a saturated voltage is applied.
In liquid crystal devices, particularly those in a birefringence mode using an optical rotatory power of a liquid crystal material as described above, inconsistencies in the cell gap (gap between substrates) cause display inconsistencies, color inconsistencies, and interference streaks to degrade display quality. When electrodes formed on the respective substrates come into contact with each other when the cell gap is narrowed by an external force, a display becomes impossible, and damages and short-circuit of a drive circuit are caused, so that controlling the cell gap so as to keep it uniform is very important.
In order to keep the cell gap uniform, inorganic substances such as glass fibers and glass beads and LCD spacers such as a particulate particle size controlling material made of an organic substance are generally used. It is necessary that these LCD spacers are used typically at a distribution density of about 15 to 100/mm.sup.3 in order to keep the cell gap uniform.
However, when spacers are present in pixels, they sometimes adversely affect display quality. For example, in a liquid crystal device in a normally white mode, when spacers are present in pixels, light passing through the spacers is always shielded by a polarizing plate on a light outputting side; therefore, a substantial opening ratio of the device decreases. On the other hand, in a liquid crystal device in a normally black mode, light passing through the spacers is not completely shielded during a black display by a polarizing plate on a light outputting side; therefore, light leakage is caused. Furthermore, it is confirmed that when remaining spacers are distributed while nonuniformly aggregating in pixels, these spacers affect the uniform orientation of liquid crystal molecules to allow disclination lines to be formed. In any of these cases, there has been the problem of decrease in contrast.
Japanese Laid-Open Patent Publication Nos. 1-233421 and 1-239527 disclose that a polymer resin is patterned in an island shape as spacers in order to keep a cell gap uniform without providing spacers in pixels. According to this method, it is possible to keep the cell gap uniform and light leakage can be prevented because of the absence of spacers in pixels. Japanese Laid-Open Patent Publication No. 64-61729 discloses a method in which a cell gap controlling material is mixed in a sealant, and only the sealant portion is pressed to attach liquid crystal substrates to each other. Japanese Laid-Open Patent Publication Nos. 61-173223, 61-184518, and 62-240930 disclose a method in which a photosensitive resin or a polymer resin is patterned to a predetermined thickness on a substrate, whereby a stripe-shaped "adductor" structure is provided thereon so as to work as spacers. Furthermore, Japanese Laid-Open Patent Publication No. 63-33730 discloses a method in which a black light shielding film is provided in gaps between pixels of a three-color filter, and the black light shielding film is provided with projections so as to work as spacers.
According to the above-mentioned methods, although spacers for keeping a cell gap can be realized, strength and shock resistance cannot be provided over a large area. Furthermore, in liquid crystal devices in which polymer walls completely surround liquid crystal regions so as to minimize the change in orientation by an external pressure, a liquid crystal material cannot be subsequently injected into the devices.
Japanese Laid-Open Patent Publication Nos. 59-222817, 3-94230, 6-194672, and 6-175133 disclose liquid crystal panels in which spacers are provided only in regions outside pixels, obtained by a photolithography process such as light exposure, development, and peeling of a photosensitive material including spherical spacers or the like, and a method for producing the same. Japanese Laid-Open Patent Publication No. 6-301040 discloses a technology in which a light-shielding film with openings is provided between a plurality of electrodes, and a photosensitive resin is exposed to light through these openings from a reverse side, whereby spacers are fixed. However, according to these technologies, since openings or regions having a low light-shielding property are formed in the light-shielding film including signal lines, contrast characteristics of an image decrease. In addition, these technologies use an alignment film formed by an alignment treatment such as rubbing for uniformly aligning liquid crystal molecules in a liquid crystal layer; therefore, an electrical breakdown is produced in active matrix devices by static electricity generated during the alignment treatment. Furthermore, when an alignment film formed in pixel regions by an alignment treatment directly comes into contact with a chemical such as a developer while a resist or the like is developed and peeled off, there is a possibility that the alignment of liquid crystal molecules and the reliability of a liquid crystal device are adversely affected.
In order to improve a display quality of liquid crystal regions, the applicant of the present application disclosed liquid crystal devices in which liquid crystal regions with liquid crystal molecules uniformly aligned therein by rubbing treatment and polymer regions are formed by polymerization and phase separation. More specifically, Japanese Patent Application No. 6-49335 discloses a technology related to a structure in which a cell gap controlling material is present in polymer walls, and Japanese Patent Application No. 6-229946 discloses a technology related to a structure in which pressure resistance of polymer walls including a cell gap controlling material is improved.
According to a method proposed by the applicant of the present application in Japanese Patent Application No. 5-30996, liquid crystal domains or liquid crystal molecules in pixel regions are axis-symmetrically aligned to realize omnidirectional viewing angle characteristics. In this liquid crystal device, for example, as shown in FIGS. 58D and 58E, liquid crystal molecules rise in the direction of each wall by the interaction between the liquid crystal molecules and the polymer walls under the application of a voltage, so that an apparent refractive index becomes almost the same in viewing directions A and B. Thus, this method has a great effect on the improvement of viewing angle characteristics. However, in order to improve viewing angle characteristics most effectively, liquid crystal molecules are required to be uniformly aligned in an axis-symmetrical manner in pixels. This makes it necessary to control cores around which liquid crystal domains are formed. Thus, it is also effective to regulate the formation of polymer walls or to form an alignment film having spherulite nulei capable of inducing the axis-symmetrical orientation of liquid crystal molecules by generating liquid crystal cores during a non-rubbing process.
Even in a method proposed by the applicant of the present application in Japanese Patent Application No. 5-30996, in a liquid crystal layer interposed between two substrates 591a and 591b, regions 16 including liquid crystal and a polymer are present between electrodes (2a and 2b) on substrates (1a and 1b) and liquid crystal regions 3 as shown in FIG. 59. Therefore, light leakage is caused by birefringence of liquid crystal molecules taken in polymer regions 4 under the application of a saturated voltage and/or liquid crystal and a polymer are not phase-separated completely. Under these circumstances, a higher degree of control of phase separation has been demanded. Furthermore, liquid crystal devices of high image quality have been demanded. In FIG. 59, the reference numeral 15 denotes a patterned polymer and the reference numeral 16 denotes adhesion (invasion) of the polymer to the liquid crystal regions 3.
Furthermore, in the case where spacers such as beads are present in pixels in order to keep a cell gap uniform, the disturbance of the orientation of liquid crystal molecules with respect to the beads is observed. In this case, an orientation state as shown in a polarizing microscope photograph of FIG. 60 is obtained; specifically, symmetry axes of axis-symmetrical orientation of liquid crystal molecules are tilted or positions of axes are shifted. When the device is observed by changing viewing directions, an area of regions corresponding to portions 7 which look black in a viewing angle direction increases in one pixel, average transmittance becomes different from that of other pixels. This is observed as roughness in a display image as a whole. Thus, in this device, it is required to strictly control symmetry axes of the orientation of the liquid crystal molecules. In any event, LCDs of higher quality are demanded.